The importance of surmounting the nonorthogonality of measured normal modes and processing shallow‐water data in such a way that modal compositions are effectively recovered for matched field processing has been demonstrated by several investigators. The potential for improvement using this technique is greatest when the nonorthogonality of the measured modes is largest. The amount by which the normal modes fail to be orthogonal for a variety of ocean bottoms, array lengths and discretizations, and array positions for the Pekeris model has been studied. Environments are selected to reflect sediment types characteristic of the continental shelf. It has been found that the nonorthogonality is greatest for water depths and frequencies at and just above modal onsets, for sound‐speed ratios close to 1, and for arrays which span only a fraction of the water column. Judicious placement and length selection for short arrays, however, can give orthogonal measured modes for some combinations of frequencies and environments when a small number of modes are present.

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